docs: fix input validation link in reactive forms (angular#56334)

PR Close angular#56334

Author: sasidharansd

adev/src/content/guide/forms/reactive-forms.md

@@ -78,7 +78,7 @@ The following example shows you how to display the current value using interpola
 The displayed value changes as you update the form control element.
 
 Reactive forms provide access to information about a given control through properties and methods provided with each instance.
-These properties and methods of the underlying [AbstractControl](api/forms/AbstractControl "API reference") class are used to control form state and determine when to display messages when handling [input validation](#basic-form-validation "Learn more about validating form input").
+These properties and methods of the underlying [AbstractControl](api/forms/AbstractControl "API reference") class are used to control form state and determine when to display messages when handling [input validation](#validating-form-input "Learn more about validating form input").
 
 Read about other `FormControl` properties and methods in the [API Reference](api/forms/FormControl "Detailed syntax reference").